A heating roller or drying drum is typically supplied with its heat-exchange medium, e.g. hot oil, via a coupling provided at the pivot axis of the roller. To this end the body in question normally has a tubular shaft extending along its pivot axis and forming a passage that connects in the coupling to a passage that in turn is connected to the supply of the heat-exchange fluid. The coupling itself has a housing that is generally stationary or at least not rotatable, and a bearing is provided that supports the shaft in the housing for rotation about its axis.
Leakage is typically prevented by providing a slide-type seal that is located to the side of the bearing toward the hot source of liquid. The bearing itself is normally a standard roller or plain bearing that is packed in heat-resistant grease.
Any leakage in such a coupling will, however, drive the heat-exchange medium through the bearing. Not only does the hot liquid heat the bearing and, possibly, drive out its lubrication, but it frequently can combine with atmospheric oxygen to damage the bearing. The seal itself can also be damaged by the leakage of the medium through it and its reaction with atmospheric oxygen.